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Abstract:

Embodiments of a suspension for a vehicle is provided. The suspension
includes, for example, a frame and a locking assembly. The locking
assembly inhibits tipping of a frame of the vehicle when tipping of the
frame is detected.

Claims:

1. A method of controlling tipping of a wheelchair frame based on downward
movement of first and second rear casters with respect to the wheelchair
frame comprising:allowing upward and downward movement of first and
second front casters relative to the frame when the first and second rear
casters are in normal operating positions relative to the frame;allowing
upward and downward movement of the first and second front casters
relative to the frame when one of the rear casters moves downward from a
normal operating position relative to the frame;inhibiting upward
movement of the first and second front casters relative to the frame when
both of the rear casters move downward from the normal operating
positions relative to the frame.

2. The method of claim 1 wherein inhibiting upward movement of the first
and second front casters relative to the frame comprises locking the
first and second front casters against upward movement relative to the
frame.

3. The method of claim 1 further comprising allowing downward movement of
the first front caster and the second front caster relative to the frame
when both of the rear casters move downward from the normal operating
positions relative to the frame.

4. The method of claim 1 further comprising biasing the first front caster
and the second front caster downward relative to the frame when both of
the rear casters move downward from the normal operating positions
relative to the frame.

5. The method of claim 1 further comprising locking the first front caster
and the second front caster against downward movement relative to the
frame when both of the rear casters move downward from the normal
operating positions relative to the frame.

6. The method of claim 1 further comprising unlocking the first front
caster and the second front caster to allow upward movement of the first
front caster and the second front caster relative to the frame when one
or more of the rear casters return to a normal operating position
relative to the frame.

7. The method of claim 1 further comprising damping upward movement of the
first and second front casters relative to the frame when one or more of
the rear casters are in a normal operating position relative to the
frame.

8. The method of claim 1 further comprising sensing the positions of the
first and second rear casters to determine whether the first and second
rear casters are in a normal operating position relative to the frame.

9. A method of controlling tipping of a wheelchair frame based on downward
movement of first and second rear casters with respect to the wheelchair
frame comprising:locking the first front caster and the second front
caster against upward movement relative to the frame when both of the
rear casters move downward from normal operating positions relative to
the frame;allowing upward movement of both the first front caster and the
second front caster relative to the frame when one of the rear casters
return to a normal operating position relative to the frame.

10. The method of claim 9 further comprising allowing downward movement of
the first front caster and the second front caster relative to the frame
when both of the rear casters move downward from the normal operating
positions relative to the frame.

11. (canceled)

12. The method of claim 9 further comprising locking the first front
caster and the second front caster against downward movement relative to
the frame when both of the rear casters move downward from the normal
operating positions relative to the frame.

13. (canceled)

14. The method of claim 9 further comprising sensing the positions of the
first and second rear casters to determine whether the first and second
rear casters are in a normal operating position relative to the frame.

15. A wheelchair comprising:a seat;a pair of drive wheels supporting the
seat;a first front caster coupled to the seat such that the first front
caster is moveable upwardly and downwardly with respect to the seat;a
second front caster coupled to the seat such that the second front caster
is moveable upwardly and downwardly with respect to the seat;a first rear
caster coupled to the seat such that the first rear caster is moveable
upwardly and downwardly with respect to the seat;a second rear caster
coupled to the seat such that the second rear caster is moveable upwardly
and downwardly with respect to the seat;at least one stabilizing assembly
coupled to the first and second front casters;at least one trigger that
controls the stabilizing assembly configured to sense positions of the
first and second rear casters;wherein the trigger causes the stabilizing
assembly to enter a disengaged state and where the stabilizing assembly
allows upward and downward movement of the first front caster and the
second front caster relative to the frame when the first rear caster
moves downward from a normal operating position relative to the frame and
the second rear caster is in a normal operating position relative to the
frame; andwherein the trigger causes the stabilizing assembly to enter an
engaged state where upward movement of the first front caster and the
second front caster relative to the frame is inhibited when both of the
rear casters move downward from normal operating positions relative to
the frame.

16. The wheelchair of claim 15 wherein the at least one stabilizing
assembly comprises a first stabilizing mechanism coupled to the first
front caster and a second stabilizing mechanism coupled to the second
front caster.

17. The wheelchair of claim 16 wherein the first and second stabilizing
mechanisms each comprise stabilizing cylinders.

18. The wheelchair of claim 17 wherein each stabilizing cylinder includes
a spring return that forces each of the front casters downward with
respect to the frame.

19. The wheelchair of claim 14 wherein the spring returns force the front
casters downward with respect to the frame when the stabilizing assembly
is engaged.

20. The wheelchair of claim 17 wherein the stabilizing cylinders damp
upward movement of the front casters relative to the frame when the
stabilizing assembly is disengaged.

21. (canceled)

22. The wheelchair of claim 16 wherein the first and second stabilizing
mechanisms are coupled such that both stabilizing mechanisms are
disengaged when the first rear caster moves downward from a normal
operating position relative to the frame and the second rear caster
remains in a normal operating position relative to the frame and both
stabilizing mechanisms are engaged when both of the rear casters move
downward from normal operating positions relative to the frame.

23. The wheelchair of claim 22 wherein the first and second stabilizing
mechanisms are mechanically coupled.

24. The wheelchair of claim 22 wherein the first and second stabilizing
mechanisms are coupled by a bar that rotates with respect to the first
and second stabilizing mechanisms when the both of the rear casters move
downwardly with respect to the frame.

25. (canceled)

26. The wheelchair of claim 22 wherein the first and second stabilizing
mechanisms are coupled by a hydraulic connection.

27. The wheelchair of claim 22 wherein the first and second stabilizing
mechanisms are electronically coupled.

28. The wheelchair of claim 15 wherein the stabilizing assembly comprises
a single stabilizing mechanism coupled to both of the front casters.

29. (canceled)

30. The wheelchair of claim 15 wherein the stabilizing assembly allows
downward movement of the first front caster and the second front caster
relative to the frame when both of the rear casters move downward from
the normal operating positions relative to the frame.

31. The wheelchair of claim 15 wherein the stabilizing assembly biases the
first front caster and the second front caster downward relative to the
frame when both of the rear casters move downward from the normal
operating positions relative to the frame.

32. The wheelchair of claim 15 wherein the stabilizing assembly locks the
first front caster and the second front caster against downward movement
relative to the frame when both of the rear casters move downward from
the normal operating positions relative to the frame.

33. The wheelchair of claim 15 wherein the stabilizing assembly allows
upward movement of the first front caster and the second front caster
relative to the frame when one or more of the rear casters return to a
normal operating position relative to the frame.

34. (canceled)

35. (canceled)

36. (canceled)

37. (canceled)

38. (canceled)

39. (canceled)

40. A wheelchair comprising:a frame;a seat supported by the frame;a pair
of drive wheels supporting the frame;a first front caster coupled to the
frame such that the first front caster is moveable upwardly and
downwardly with respect to the frame;a second front caster coupled to the
frame such that the second front caster is moveable upwardly and
downwardly with respect to the frame;a first rear caster coupled to the
frame such that the first rear caster is moveable upwardly and downwardly
with respect to the frame;a second rear caster coupled to the frame such
that the second rear caster is moveable upwardly and downwardly with
respect to the frame;a stabilizing assembly coupled to the first and
second front casters;a trigger in communication with the stabilizing
assembly;wherein the stabilizing assembly inhibits the first front caster
and the second front caster from moving upward relative to the frame when
the trigger senses that both of the rear casters have moved downward from
normal operating positions relative to the frame; andwherein the
stabilizing assembly allows upward movement of the first front caster and
the second front caster relative to the frame when the trigger senses
that one or more of the rear casters have returned to a normal operating
position relative to the frame.

41. The wheelchair of claim 40 wherein the stabilizing assembly comprises
a first stabilizing mechanism coupled to the first front caster and a
second stabilizing mechanism coupled to the second front caster.

42. (canceled)

43. (canceled)

44. (canceled)

45. (canceled)

46. The wheelchair of claim 42 wherein the stabilizing cylinders allow
downward movement of the front casters with respect to the frame when the
stabilizing assembly is engaged.

47. (canceled)

48. (canceled)

49. (canceled)

50. (canceled)

51. (canceled)

52. (canceled)

53. The wheelchair of claim 40 wherein the stabilizing assembly comprises
a single stabilizing mechanism coupled to both of the front casters.

54. (canceled)

55. (canceled)

56. (canceled)

57. The wheelchair of claim 40 wherein the stabilizing assembly locks the
first front caster and the second front caster against downward movement
relative to the frame when both of the rear casters move downward from
the normal operating positions relative to the frame.

58. (canceled)

59. (canceled)

60. (canceled)

61. (canceled)

62. (canceled)

63. (canceled)

64. (canceled)

65. (canceled)

66. (canceled)

67. (canceled)

68. (canceled)

69. (canceled)

70. (canceled)

71. (canceled)

72. (canceled)

73. (canceled)

74. (canceled)

75. (canceled)

76. (canceled)

77. (canceled)

78. (canceled)

79. (canceled)

80. (canceled)

81. (canceled)

82. (canceled)

83. (canceled)

84. (canceled)

85. (canceled)

86. (canceled)

87. (canceled)

88. (canceled)

89. (canceled)

90. (canceled)

91. (canceled)

92. (canceled)

93. (canceled)

Description:

RELATED APPLICATIONS

[0001]This application claims the benefit of U.S. provisional patent
application Ser. No. 60/901,513 for STABILITY CONTROL SYSTEM filed Feb.
14, 2007, the entire disclosure of which is fully incorporated herein by
reference.

BACKGROUND

[0002]Wheelchairs and scooters are an important means of transportation
for a significant portion of society. Whether manual or powered, these
vehicles provide an important degree of independence for those they
assist. However, this degree of independence can be limited if the
wheelchair is required to traverse obstacles such as, for example, curbs
that are commonly present at sidewalks, driveways, and other paved
surface interfaces. This degree of independence can also be limited if
the vehicle is required to ascend inclines or descend declines.

[0003]Most wheelchairs have front and rear casters to stabilize the chair
from tipping forward or backward and to ensure that the drive wheels are
always in contact with the ground. The caster wheels are typically much
smaller than the driving wheels and located both forward and rearward of
the drive wheels. Though this configuration provides the wheelchair with
greater stability, it can hamper the wheelchair's ability to climb over
obstacles such as, for example, curbs or the like, because the size of
the front casters limits the height of the obstacle that can be
traversed.

[0004]Though equipped with front and rear suspended casters, most
mid-wheel drive wheelchairs exhibit various degrees of tipping forward or
rearward when descending declines or ascending inclines. This is because
the suspensions suspending the front or rear stabilizing casters are
compromised so that they are not made too rigid, which would prevent
tipping and also not provide much suspension, or are made too flexible
thereby effectively not providing any degree of suspension or
stabilization.

SUMMARY

[0005]According to one embodiment, a suspension for a vehicle is provided.
The suspension includes, for example, a stabilizing assembly. The
stabilizing assembly inhibits tipping of a frame of the vehicle when
tipping of the frame is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]In the accompanying drawings which are incorporated in and
constitute a part of the specification, embodiments of tip or stability
control systems, sub-assemblies, and components are illustrated, which
together with a general description given above and the detailed
description given below, serve to explain the principles of tip or
stability control systems, sub-assemblies and components.

[0007]FIG. 1A is an illustration of a rear of an embodiment of a mid-wheel
drive wheelchair;

[0008]FIG. 1B is a view taken along lines 1B-1B in FIG. 1A, illustrating a
side of the mid-wheel drive wheelchair;

[0009]FIG. 1C is a view taken along lines 1C-1C in FIG. 1B, illustrating a
front of the mid-wheel drive wheelchair;

[0010]FIG. 2 is a flow chart that illustrates an embodiment of a method of
controlling tipping of a mid-wheel drive wheelchair frame;

[0011]FIGS. 3A-3C illustrate the wheelchair of FIGS. 1A-1C, where one rear
caster has moved downward relative to a frame;

[0012]FIGS. 4A-4C illustrate the wheelchair of FIGS. 1A-1C, where the
wheelchair is exhibiting a tipping behavior;

[0013]FIG. 5 is an illustration of an embodiment of a wheelchair with a
fluid cylinder stabilizing assembly;

[0014]FIG. 6 is an illustration of an embodiment of a wheelchair with a
fluid cylinder with spring return stabilizing assembly;

[0015]FIGS. 7A-7C illustrate an embodiment of a mid-wheel drive wheelchair
that is similar to the wheelchair shown in FIGS. 1A-1C where two
stabilizing members are linked;

[0016]FIGS. 8A-8C illustrate an embodiment of a mid-wheel drive wheelchair
that is similar to the wheelchair shown in FIGS. 1A-1C that includes a
single stabilizing member or assembly;

[0017]FIGS. 9A-9C illustrate an embodiment of a mid-wheel drive wheelchair
that is similar to the wheelchair shown in FIGS. 1A-1C where two triggers
or sensors are linked;

[0018]FIGS. 10A-10C illustrate an embodiment of a mid-wheel drive
wheelchair that is similar to the wheelchair shown in FIGS. 1A-1C that
includes a single trigger or sensor;

[0019]FIGS. 11A-11C illustrate an embodiment of a mid-wheel drive
wheelchair that is similar to the wheelchair shown in FIGS. 1A-1C that
includes a rear caster position sensing linkage coupled to a single
trigger or sensor that indicates when both rear casters drop relative to
a frame;

[0020]FIGS. 12A-12C illustrate the wheelchair of FIGS. 11A-11C, where one
rear caster has moved downward relative to a frame;

[0021]FIGS. 13A-13C illustrate the wheelchair of FIGS. 11A-11C, where the
wheelchair is exhibiting a tipping behavior;

[0022]FIGS. 14A-14C illustrate an embodiment of a mid-wheel drive
wheelchair that is similar to the wheelchair shown in FIGS. 1A-1C that
includes a rear caster position sensing linkage coupled to a pair of
triggers or sensor that indicates when both rear casters drop relative to
a frame;

[0023]FIGS. 15A-15C illustrate the wheelchair of FIGS. 14A-14C, where one
rear caster has moved downward relative to a frame;

[0024]FIGS. 16A-16C illustrate the wheelchair of FIGS. 14A-14C, where the
wheelchair is exhibiting a tipping behavior;

[0025]FIG. 17A illustrates a rear view of an embodiment of a rear caster
suspension with a rear caster position sensing arrangement;

[0026]FIG. 17B is a view taken along lines 17B-17B in FIG. 17A,
illustrating a side view of the rear caster suspension and rear caster
position sensing arrangement;

[0027]FIG. 17C is a view taken along lines 17C-17C in FIG. 17A,
illustrating a top view of the rear caster suspension and rear caster
position sensing arrangement;

[0028]FIGS. 18A and 18B illustrate the rear caster suspension and rear
caster position sensing arrangement of FIGS. 17A-17C, where one rear
caster has moved downward;

[0029]FIGS. 19A and 19B illustrate the rear caster suspension and rear
caster position sensing arrangement of FIGS. 17A-17C, where both rear
casters have moved downward;

[0030]FIGS. 20A-20C illustrate an embodiment of a rear caster suspension
and rear caster position sensing arrangement that is similar to the rear
caster suspension and rear caster position sensing arrangement shown in
FIGS. 17A-17C where movement of a first rear caster pivot arm depends on
a position of a second rear caster pivot arm;

[0031]FIGS. 21A and 21B illustrate the rear caster suspension and rear
caster position sensing arrangement of FIGS. 20A-20C, where one rear
caster has moved downward;

[0032]FIGS. 22A and 22B illustrate the rear caster suspension and rear
caster position sensing arrangement of FIGS. 20A-20C, where further
downward movement of one rear caster is inhibited by a second rear
caster;

[0033]FIG. 23A illustrates a rear of an embodiment of a rear caster
suspension and rear caster position sensing arrangement;

[0034]FIG. 23B is a view taken along lines 23B-23B in FIG. 23A,
illustrating a side of the rear caster suspension and rear caster
position sensing arrangement;

[0035]FIG. 23C is a view taken along lines 23C-23C in FIG. 23A,
illustrating a top of the rear caster suspension and rear caster position
sensing arrangement;

[0036]FIGS. 24A-24C illustrate the rear caster suspension and rear caster
position sensing arrangement of FIGS. 23A-23C, where downward movement of
one rear caster is inhibited by a second rear caster;

[0037]FIGS. 25A-25C illustrate an embodiment of a rear caster suspension
and rear caster position sensing arrangement that is similar to the rear
caster suspension and rear caster position sensing arrangement of FIGS.
23A-23C, where the rear casters are connected to a pivotable arm;

[0038]FIG. 26 illustrates an embodiment of a mid-wheel drive wheelchair
that includes a tip or stability control system and front caster pivot
arm that are coupled to drive assemblies;

[0039]FIG. 27 illustrates an embodiment of a mid-wheel drive wheelchair
that includes a tip or stability control system and front caster pivot
arms that are coupled to drive assemblies;

[0040]FIG. 28 illustrates an embodiment of a mid-wheel drive wheelchair
that includes a tip or stability control system and front caster pivot
arms that are coupled to drive assemblies;

[0041]FIG. 29 illustrates an embodiment of a mid-wheel drive wheelchair
that includes a tip or stability control system and front caster pivot
arms that are coupled to drive assemblies;

[0042]FIG. 30 illustrates an embodiment of a mid-wheel drive wheelchair
that includes a tip or stability control system and front caster pivot
arms that are coupled to drive assemblies;

[0043]FIG. 31 illustrates an embodiment of a mid-wheel drive wheelchair
that includes a tip or stability control system and front caster pivot
arms that are coupled to drive assemblies;

[0044]FIG. 32 is a perspective view of an embodiment of a mid-wheel drive
wheelchair that includes a tip or stability control system;

[0045]FIG. 33 is a side view of the mid-wheel drive wheelchair of FIG. 32;

[0046]FIG. 34 is a view taken along lines 34-34 in FIG. 33;

[0047]FIG. 35 is a view taken along lines 35-35 in FIG. 33;

[0048]FIG. 36 is a view taken along lines 36-33 in FIG. 33;

[0049]FIG. 37 is a view taken along lines 37-37 in FIG. 33;

[0050]FIG. 38 is a view of the wheelchair of FIG. 32 with components
removed;

[0051]FIG. 39 is a side view of the mid-wheel drive wheelchair with
components removed of FIG. 38;

[0062]FIG. 49A is a view similar to FIG. 49, where the rear caster
position sensing arrangement has moved to an engaged position; and

[0063]FIG. 50 is a view taken along lines 50-50 in FIG. 45.

DETAILED DESCRIPTION

[0064]The present description provides multiple embodiments of suspension
systems for vehicles, such as, wheelchairs, including, but not limited to
mid-wheel drive wheelchairs, scooters, and other personal mobility
vehicles. The drawings illustrate the suspension systems on mid-wheel
drive wheelchairs. However, the described suspensions can be implemented
on any personal mobility vehicle, including scooters and rear drive
wheelchairs.

[0065]The suspension systems include a tip or stability control system.
Generally, the control system includes a trigger or sensor for sensing
when conditions exist that may cause the vehicle to exhibit a tipping
behavior, which can be either forward or rearward, and a stabilizing
member or assembly that stabilizes the suspension system to prevent any
further tipping behavior. The trigger or sensor also senses when the
vehicle is no longer subject to conditions that may cause it to exhibit a
tipping behavior and causes the stabilizing member or assembly to no
longer inhibit movement of the suspension system. A variety of different
control system features are disclosed in the context of the following
exemplary embodiments. The individual features of the following
embodiments may be used alone or in combination with features of other
embodiments.

[0066]One feature of some control system embodiments disclosed herein is
that upward movement of one front caster is inhibited to prevent tipping
only if upward movement of the other front caster is also inhibited.
Another feature of some control system embodiments disclosed herein is
that the relative positions of two rear casters are sensed to determine a
tipping behavior. For example, a tipping behavior may be indicated only
when both rear casters move downward relative to a frame.

[0067]FIGS. 1A, 1B, and 1C schematically illustrate a mid-wheel drive
wheelchair 100 that includes a tip or stability control system that
comprises one or more sensors 112 and one or more stabilizing members or
assemblies 114. The control system 100 can also be applied to a wide
variety of other vehicles, including but not limited to, rear drive wheel
chairs, front drive wheel chairs, scooters, and other personal mobility
vehicles. The wheelchair 100 includes a frame 102, a seat 104 supported
by the frame, first and second drive wheels 106 that support the frame,
first and second front casters 108a, 108b, first and second rear casters
110a, 110b, one or more sensors 112, and one or more stabilizing members
or assemblies 114. In this application, the term "frame" refers to any
component or combination of components that are configured for mounting
of a drive assembly and a caster pivot arm. The first and second front
casters 108a, 108b are coupled to the frame 102 such that the front
casters are moveable upwardly and downwardly with respect to the frame as
indicated by double arrow 116. In the example illustrated by FIGS. 1A,
1B, and 1C, the front casters are independently coupled to the frame 102
by separate pivot arms 118a, 118b. In another embodiment, the pivot arms
118a, 118b are coupled such that movement of one pivot arm is transferred
to the other pivot arm. For example, a torsion bar (not shown) may couple
the pivot arms 108a, 108b. The first and second rear casters 110a, 110b
are coupled to the frame 102 such that the rear casters are moveable
upwardly and downwardly with respect to the frame. In the example
illustrated by FIGS. 1A, 1B, and 1C, the rear casters are independently
coupled to the frame 102 by separate rear caster pivot arms 120a, 120b.
In another embodiment, the rear caster pivot arms 120a, 120b are coupled
such that movement of one pivot arm is transferred to the other pivot arm
(See the embodiment of FIG. 23 for example).

[0068]One stabilizing member 114 is coupled to each front caster pivot
arms 118a, 118b and to the frame 102. However, any number of stabilizing
members 114 can be used, may take any form, and may be coupled to the
front caster pivot arm and the frame in any manner that allows the
stabilizing member or members to inhibit movement of one or more of the
front caster pivot arms with respect to the frame in at least one
direction. Examples of stabilizing members that may be used include, but
are not limited to, the stabilizing members disclosed herein and the
locking members disclosed in U.S. Pat. No. 6,851,711 to Goertzen et al,
United States Patent Application Publication No. 2004/0150204, and United
States Patent Application Publication No. 2005/0151360 to Bertrand et
al., which are all incorporated herein by reference in their entireties.

[0069]One trigger or sensor 112 is coupled to each of the rear caster
pivot arms 120a,b in the example illustrated by FIGS. 1A, 1B, and 1C.
However, any number of triggers or sensors 112 can be used, may take any
form and may be positioned in any way that allows tipping of the frame
102 to be sensed. Examples of triggers or sensors that may be used
include, but are not limited to, the triggers or sensors disclosed herein
and the triggers or sensors disclosed in U.S. Pat. No. 6,851,711 to
Goertzen et al, United States Patent Application Publication No.
2004/0150204, and United States Patent Application Publication No.
2005/0151360 to Bertrand et al. Tipping may be sensed in ways that are
unrelated to movement of the rear casters relative to the frame. Examples
of ways a tipping behavior may be sensed include, but are not limited to,
the ways tipping is sensed in U.S. Pat. No. 6,851,711 to Goertzen et al,
United States Patent Application Publication No. 2004/0150204, and United
States Patent Application Publication No. 2005/0151360 to Bertrand et al.

[0070]FIG. 2 is a flow chart that illustrates an embodiment of a method
200 of stabilizing a mid-wheel drive wheelchair frame. In the method,
upward and downward movement of the front casters 108a, 108b is allowed
(block 202) when at least one rear caster 110a, 110b is in a normal
operating position. When both of the rear casters 110a, 110b move out of
a normal operating position, the front casters 108a, 108b are locked
(block 204) against at least upward movement relative to the frame. The
front casters 108a, 108b may be locked against both upward and downward
movement or only against upward movement.

[0071]Normal operating positions of the rear casters 110a and 110b include
the positions of the rear casters when the wheelchair is stationary on
level ground (referred to herein as the stationary, level ground
position). Normal operating positions of the rear casters 110a and 110b
also include any position of the rear casters relative to the frame where
the rear caster(s) are rotated as indicated by arrow 70 in FIG. 1B.
Normal operating positions of the rear casters 110a, 110b also include
any positions where the rear caster(s) are rotated relative to the frame
102 as indicated by arrow 72 by less than a predetermined distance or
angle below the stationary, level ground position. In the exemplary
embodiment, the predetermined distance or angle from the stationary,
level ground position in the direction indicated by arrow 72 corresponds
to a distance or angle that is indicative of a tipping behavior of the
wheelchair. For example, movement of the rear caster(s) relative to the
frame in the direction indicated by arrow 72 that is greater than 1/2
inch may be indicative of tipping of the wheelchair and out of the normal
operating position of the rear casters. However, the normal operating
position of the rear casters 110a and 110b will vary from one wheelchair
to another.

[0072]FIGS. 1, 3 and 4 illustrate a 100 wheelchair with a stabilizing
assembly 114 that inhibits upward movement of the first and second front
casters 108a, 108b with respect to the wheelchair frame 102 based on
movement of first and second rear casters 110a, 110b with respect to the
wheelchair frame. Referring to FIGS. 1A, 1B and 1C, the stabilizing
assembly 114 allows upward and downward movement (as indicated by double
arrow 116) of the first and second front casters 108a, 108b relative to
the frame 102 when the first and second rear casters 110a, 110b are in
normal operating positions relative to the frame.

[0073]FIGS. 3A, 3B, and 3C illustrate the wheelchair 100 where the rear
caster 110a is in a normal operating position and the rear caster 110b
has dropped below the range of normal operating positions. This condition
may occur when one of the rear casters falls into a depression 302 as
illustrated by FIGS. 3A, 3B, and 3C. This condition may also occur when
the wheelchair travels laterally along an inclined surface. When the rear
caster 110a is in a normal operating position and the rear caster 110b
has dropped below the range of normal operating positions, both of the
stabilizing members 114 continue to allow upward and downward movement of
the first and second front casters 108a, 108b relative to the frame 102.

[0074]FIGS. 4A, 4B, and 4C illustrate the wheelchair 100 exhibiting a
tipping behavior. The frame 102 of the wheelchair 100 is pitched forward
toward the front casters 108a, 108b. As a result, the rear casters 110a,
110b move downward relative to the frame 102 to maintain contact with the
ground. This downward movement positions both of the rear casters 110a,
110b below the range of normal operating positions relative to the frame
102. The sensors or triggers 112 sense that the rear casters 110a, 110b
are both below the range of normal operating positions and cause the
stabilizing members 114 to engage. In the example illustrated by FIGS.
4A, 4B and 4C, engagement of the stabilizing assemblies locks the first
and second front casters 108a, 108b against upward movement relative to
the frame, but allow the front casters to move downward as indicated by
arrow 400 when the stabilizing assembly is engaged. In another
embodiment, the stabilizing assembly 114 locks the front caster pivot
arms against both upward and downward movement with respect to the pivot
arm when engaged. In another embodiment, engagement of the stabilizing
assemblies 114 greatly increase the amount of force required to move the
front casters upward with respect to the frame. In another embodiment,
engagement of the stabilizing assemblies 114 causes the stabilizing
assemblies to apply additional force to move the front casters downward
relative to the frame and return the frame to a normal operating
position. When one or more of the rear casters return to a normal
operating position relative to the frame, the sensors or triggers 112
disengage the stabilizing assembly to allow upward and downward movement
of the first and second front casters relative to the frame.

[0075]The stabilizing member, stabilizing members, or stabilizing assembly
114 or assemblies can take a wide variety of different forms. For
example, the stabilizing assembly 114 may be a fluid cylinder 500 as
illustrated by FIG. 5. One fluid cylinder 500 may be coupled between each
front caster 108a, 108b at connection 501 and the frame 102 at connection
503, or a single fluid cylinder may be coupled between the front casters
and the frame. As used herein, "coupled" refers to both direct coupling
of two or more components or the indirect coupling of components such as
through one or more intermediary components or structures. The fluid
cylinder 500 includes a piston 502, a housing 504 that defines a piston
chamber 506, a rod 508, and a valve 510. The rod 508 extends into the
housing 504 and is connected to the piston. The piston 502 divides the
chamber 506 into two compartments 512, 514. The valve 510 selectively
allows fluid to flow between the two compartments when the valve is open
and prevents flow between the two compartments when the valve is closed.
As such, the rod 508 can move into and out of the housing 504 when the
valve 510 is open and the position of the piston 502 and the rod is
substantially fixed when the valve is closed. When the valve 510 is open,
the movement of the fluid between the chambers 512, 514 and through the
valve 510 provides a damping effect. As such, the cylinder 500 acts as a
shock absorber when the valve is open and damps upward and downward
movement of the front caster. In one embodiment, when the valve is
"closed" fluid is allowed flow from the compartment 512 to the
compartment 514, but not from the compartment 514 to the compartment 512.
As such, the rod 508 may be moved into the housing 504, but not out the
housing when the valve 510 is closed. When the valve 510 is closed, the
cylinder 500 damps downward movement of the front caster and inhibits
upward movement of the front caster. One acceptable fluid cylinder that
may be used is model number Koa8kx-2-06-304/000N from Easylift.

[0076]FIG. 6 illustrates a cylinder 600 that is similar to the cylinder
500 illustrated in FIG. 5, but includes a spring 602 that biases or
returns the rod 508 to a retracted position. In an embodiment where the
valve prevents fluid flow between the compartments 512, 514 when the
valve is closed, the actuator 600 biases the front caster toward contact
with the ground only when the valve 510 is open. In an embodiment where
the valve allows flow from the compartment 512 to the compartment 514,
but not from the compartment 514 to the compartment 512 when the valve is
closed, the actuator 600 biases the front caster toward contact with the
ground when the valve 510 is open or closed. One acceptable fluid
cylinder with a spring return that may be used is model number
k0m2pm2-060-345-002/50N from Easylift.

[0077]The stabilizing cylinders 500, 600 illustrated by FIGS. 5 and 6 are
two examples of the wide variety of different stabilizing assemblies 114
that can be used. Any arrangement capable of inhibiting upward and/or
downward movement of a front caster relative to a frame can be used. As
noted above, any of the arrangements for inhibiting movement of a front
caster with respect to a frame disclosed in U.S. Pat. No. 6,851,711 to
Goertzen et al., United States Patent Application Publication No.:
2004/0150204 to Goertzen et al., and United States Patent Application
Publication No.: 2005/0151360 to Bertrand et al. can be used.

[0078]Stabilizing members or assemblies 114 and triggers or sensors 112
may be arranged in a wide variety of different ways to inhibit further
tipping when both rear casters 110a, 110b drop below the range of normal
operating positions. Referring to FIGS. 7A, 7B, and 7C a trigger or
sensor 112 is coupled to each rear caster 110a, 110b. A stabilizing
member or assembly 114 is coupled to each front caster 108a, 108b. The
stabilizing assemblies 114 are linked by a coupling 700, such that each
stabilizing member or assembly 114 will not engage unless the other
stabilizing assembly also engages. The coupling 700 may take a wide
variety of different forms. For example, the coupling 700 may be a
mechanical linkage, and electronic linkage, an electromechanical linkage
or a pneumatic or hydraulic linkage. The stabilizing members or
assemblies 114 may be mechanically linked by wire, a rod or a clutch
mechanism, electromechanically linked by a pair of solenoid actuators
that are in electronic communication. When the stabilizing assemblies 114
are fluid actuators, the stabilizing assemblies may be pneumatically or
hydraulically linked by conduits and valves that connect the chambers of
the fluid actuators. For example, fluid devices from Easylift may be
linked in this manner.

[0079]In the example illustrated by FIGS. 8A, 8B, and 8C a trigger or
sensor 112 is coupled to each rear caster 110a, 110b and a single
stabilizing assembly 114 is coupled to both of the front casters 108a,
108b. The stabilizing member or assembly 114 is in communication with
both triggers or sensors 112, such that the stabilizing assembly 114 will
not engage unless both of the triggers or sensors 112 sense a condition
that indicates a tipping behavior of the frame 102, such as downward
movement of both rear casters 110a, 110b relative to the frame 102. The
single stabilizing assembly 114 may be arranged to permit independent
upward and downward movement of the front casters 108a, 108b.

[0080]In the examples illustrated by FIGS. 9A, 9B and 9C, a trigger or
sensor 112 is coupled to each rear caster 110a, 1110b and a stabilizing
assembly 114 is coupled to each front caster 108a, 108b. The triggers or
sensors 112 are linked by a coupling 900, such that each sensor or
trigger will not cause engagement of its respective stabilizing assembly
114 unless both of the sensors or triggers sense a tipping behavior of
the wheelchair. The coupling 900 may take a wide variety of different
forms. For example, the coupling 900 may be a mechanical linkage, and
electronic linkage, an electromechanical linkage or a pneumatic or
hydraulic linkage. The triggers or sensors 112 may be mechanically linked
by wire or a rod, electromechanically linked by a pair of solenoid
actuators that are in electronic communication, and/or pneumatically or
hydraulically linked by a pair of fluid actuators that are in fluid
communication.

[0081]In the example illustrated by FIGS. 10A, 10B, and 10C a single
trigger or sensor 112 is coupled to both rear casters 110a, 110 and a
single stabilizing assembly 114 is coupled to both of the front casters
108a, 108b. The single stabilizing assembly 114 is controlled by the
single trigger or sensor 112. In one embodiment, the single trigger or
sensor 112 will not detect a tipping behavior unless both rear casters
fall below their range of normal operating positions. Tie single trigger
or sensor 112 causes the single stabilizing assembly 114 to engage when a
tipping behavior is sensed. The single stabilizing assembly 114 may be
arranged to permit independent upward and downward movement of the front
casters 108a, 108b when disengaged and independent downward movement of
the front casters when engaged.

[0082]FIGS. 11, 12 and 13 illustrate a wheelchair 1100 with a rear caster
position sensing linkage 1101 that allows a single trigger or sensor 112
to determine when both of the rear casters 110a, 110b have dropped below
their normal operating positions with respect to the frame 102. The
linkage 1101 and sensor 112 can be used to control a pair of stabilizing
members 114 as illustrated, or a single stabilizing member (see FIG. 10).
The linkage 1101 is pivotally connected to the frame at pivot point 1102.
The linkage 1101 includes a rear caster pivot arm sensing portion 1104
and a sensor activating portion 1106. The rear caster pivot arm sensing
portion 1104 and a sensor activating portion 1106 are pivotable around
the pivot point 1102. The sensing portion 1104 is in connection with the
rear caster pivot arms 120a, 120b. The sensor activating portion 1106 is
in communication with the trigger or sensor 112.

[0083]Referring to FIGS. 11A, 11B and 11C, when the first and second rear
casters 108a, 108b are in normal operating positions, the first and
second rear caster pivot arms 120a, 120b maintain the rear caster pivot
arm sensing portion 1104 and the sensor activating portion 1106 in a
first or disengaged position shown in FIGS. 11A, 11B, and 11C. When the
sensor activating portion 1106 is in the first position, the sensor 112
controls the stabilizing assembly 114 to allow upward and downward
movement (as indicated by double arrow 1116) of the first and second
front casters 108a, 108b relative to the frame 102. In the example
illustrated by FIGS. 11A, 11B, and 11C, the sensor activating portion
1106 is in engagement or close to the sensor in the first or disengaged
position. In another embodiment, the sensor activating portion 1106 is
spaced apart from the sensor in the first position or disengaged
position.

[0084]FIGS. 12A, 12B, and 12C illustrate the wheelchair 1100 where the
rear caster 110a is in a normal operating position and the rear caster
110b has dropped below the range of normal operating positions. When the
rear caster 110a is in a normal operating position and the rear caster
110b has dropped below the range of normal operating positions, the first
rear caster pivot arms 120a maintains the rear caster pivot arm sensing
portion 1104 and the sensor activating portion 1106 in the first or
disengaged position.

[0085]FIGS. 13A, 13B, and 13C illustrate the wheelchair 100 exhibiting a
tipping behavior. The frame 102 of the wheelchair 100 is pitched forward
toward the front casters 108a, 108b. As a result, the rear casters 110a,
110b move downward relative to the frame 102 to maintain contact with the
ground. This downward movement positions both of the rear casters 110a,
110b below the range of normal operating positions with respect to the
frame. When the first and second rear casters 108a, 108b fall below their
ranges of normal operating positions, the rear caster pivot arm sensing
portion 1104 and the sensor activating portion 1106 pivot to a second or
engaged position shown in FIGS. 13A, 13B, and 13C. When the sensor
activating portion 1106 is in the second or engaged position, the sensor
112 controls the stabilizing assembly 114 to inhibit at least upward
movement of the first and second front casters 108a, 108b relative to the
frame 102. In the example illustrated by FIGS. 13A, 13B, and 13C, the
sensor activating portion 1106 is spaced apart from the sensor in the
second or engaged position. In another embodiment, the sensor activating
portion 1106 is in contact or close to the sensor in the second or
engaged position. When one or more of the rear casters return to a normal
operating position relative to the frame, the linkage 1101 is moved back
to the disengaged position and the sensor or trigger 114 causes the
stabilizing assembly to disengage and allow upward and downward movement
of the front casters relative to the frame.

[0086]FIGS. 14, 15 and 16 illustrate a wheelchair 1400 with a rear caster
position sensing linkage 1401 that actuates a pair of triggers or sensors
112 when both of the rear casters 110a, 110b have dropped below their
normal operating positions with respect to the frame 102 and does not
actuate either of the triggers or sensors 112 when one or more of the
rear casters 110a, 110b are in their normal operating position with
respect to the frame 102. The linkage 1401 and sensors 112 can be used to
control a pair of stabilizing members 114 as illustrated, or a single
stabilizing member (see FIG. 8). The linkage 1401 is pivotally connected
to the frame at pivot point 1402. The linkage 1401 includes a rear caster
pivot arm sensing portion 1404 and a sensor activating portion 1406. The
rear caster pivot arm sensing portion 1404 and a sensor activating
portion 1406 are pivotable around the pivot point 1402. The sensing
portion 1404 is coupled to the rear caster pivot arms 120a, 120b. The
sensor activating portion 1406 is in communication with both of the
triggers or sensors 112.

[0087]Referring to FIGS. 14A, 14B and 14C, when the first and second rear
casters 108a, 108b are in normal operating positions, the first and
second rear caster pivot arms 120a, 120b maintain the rear caster pivot
arm sensing portion 1404 and the sensor activating portion 1406 in a
first or engaged position shown in FIGS. 14A, 14B, and 14C. When the
sensor activating portion 1406 is in the first position, the sensor
activating portion 1406 maintains both sensors 112 in a first state. In
the first state, the two sensors 112 control the stabilizing assemblies
114 to allow upward and downward movement (as indicated by double arrow
1416) of the first and second front casters 108a, 108b relative to the
frame 102.

[0088]FIGS. 15A, 15B, and 15C illustrate the wheelchair 1400 where the
rear caster 110a is in a normal operating position and the rear caster
110b has dropped below the range of normal operating positions. When the
rear caster 110a is in a normal operating position and the rear caster
110b has dropped below the range of normal operating positions, the first
rear caster pivot arm 120a maintains the rear caster pivot arm sensing
portion 1404 and the sensor activating portion 1106 in the first or
disengaged position.

[0089]FIGS. 16A, 16B, and 16C illustrate the wheelchair 1400 exhibiting a
tipping behavior. The rear casters 110a, 110b move downward, below the
range of normal operating positions relative to the frame. When the first
and second rear casters 108a, 108b fall below their ranges of normal
operating positions, the rear caster pivot arm sensing portion 1404 and
the sensor activating portion 1406 move to a second or engaged position
shown in FIGS. 16A, 16B, and 16C. When the sensor activating portion 1406
is in the second or engaged position, the sensor activating portion 1406
places both sensors 112 in a second state. In the second state, the
sensors 112 control the stabilizing assemblies 114 to inhibit at least
upward movement of the first and second front casters 108a, 108b relative
to the frame 102. When one or more of the rear casters return to a normal
operating position relative to the frame, the linkage 1401 is moved back
to the disengaged position and both sensors or triggers 114 cause the
stabilizing assemblies 114 to disengage and allow upward and downward
movement of the front casters relative to the frame.

[0090]FIGS. 17, 18 and 19 illustrate an embodiment of a rear caster
suspension 1700 with a rear caster position sensing arrangement 1706. The
rear caster suspension 1700 includes a pair of rear caster assemblies
1702a, 1702b, a pair of sensors or triggers 1704a, 1704b, the rear caster
position sensing arrangement 1706, and a pair of biasing members 1708a,
1708b, such as springs or other resilient members. The rear caster
position sensing arrangement 1706 is in communication with both rear
caster assemblies 1702a, 1702b. When one or both of the rear casters
1702a, 1702b are in a normal operating position, the rear caster position
sensing arrangement communicates this condition to both sensors or
triggers 1704a, 1704b. When both of the rear casters 1704a, 1704b fall
below their normal operating positions, the rear castor position sensing
arrangement communicates this condition to both sensors or triggers 104a
and 104b. As a result, both sensors or triggers 1704a, 1704b are placed
in an engaged state when both rear casters 1702a, 1702b fall below their
normal operating positions and both sensors or triggers 1704a, 1704b are
placed in a disengaged state when one or both of the rear casters are in
a normal operating position. The conditions of the rear casters can be
communicated by the rear caster position sensing arrangement in a wide
variety of different ways. For example, the rear caster position sensing
arrangement may be a mechanical linkage or assembly that communicates the
condition of the rear casters to the sensors, as illustrated by FIGS.
17A-17C.

[0091]In the example illustrated by FIGS. 17, 18 and 19, compression
springs are schematically represented. However, extension springs can be
used, or the biasing members can take some other form. Each rear caster
assembly 1702 includes a caster 1710 and a pivot arm 1712. The castor
1710 is rotatable about an axis 1714 with respect to the pivot arm 1712.
The pivot arms 1712 are coupled to a wheelchair frame 1701 (See FIG. 17B)
at pivots 1716a, 1716b. The sensors or triggers 1704a, 1704b are
supported by the wheelchair frame 1701.

[0092]The illustrated rear caster position sensing arrangement 1706
includes a pair of spaced apart trigger actuating members 1720a, 1720b
that are coupled to the wheelchair frame 1701 at pivots 1722a, 1722b. The
trigger actuating members 1720a, 1720b are connected together by a bar
1724. The biasing members 1708a, 1708b are interposed between the rear
caster assemblies 1702a, 1702b and the trigger actuating members 1720a,
1720b.

[0093]The rear caster suspension 1700 and rear caster position sensing
arrangement 1706 can be included on any type of wheelchair to sense a
tipping behavior and control one or more stabilizing members or a
stabilizing assembly to inhibit further tipping. Referring to FIGS. 17A,
17B and 17C, when the rear caster assemblies 1702a, 1702b are in normal
operating positions relative to the frame, 1701, the biasing members
1708a, 1708b are compressed between the trigger actuating members 1720a,
1720b and the rear caster pivot arms 1712a, 1712b. The biasing members
1708a, 1708b force the trigger actuating members 1708a, 1708b into
engagement with the sensors or triggers 1704a, 1704b to place both of the
sensors in a depressed or disengaged state.

[0094]FIGS. 18A and 18B illustrate the rear caster suspension 1700 and
rear caster position sensing arrangement 1706 where the rear caster
assembly 1702b is in a normal operating position and the rear caster
assembly 1702a has dropped below the range of normal operating positions.
This condition may occur when the wheelchair travels laterally along an
inclined surface 1800. This condition may also occur when one of the rear
casters falls into a depression (see FIGS. 3A, 3B, and 3C). When the rear
caster assembly 1702b is in a normal operating position and the rear
caster assembly 1702a has dropped below the range of normal operating
positions, the biasing member 1708b remains compressed between the
trigger actuating member 1720b and the rear caster pivot arms 1712b,
while the biasing member 1708a extends to a relaxed state (See FIG. 18B).
The biasing member 1708b forces the trigger actuating member 1720b into
engagement with the sensor or trigger 1704b. The bar 1724 that connects
the trigger actuating member 1720a to the trigger actuating member 1720b
holds the trigger actuating member 1720a in engagement with the sensor or
trigger 1704a. The trigger actuating members 1720a, 1720b place both of
the sensors in a depressed or disengaged state when the rear casters are
in the positions shown in FIGS. 18A and 18B.

[0095]FIGS. 19A and 19B illustrate the rear caster suspension 1700 and
rear caster position sensing arrangement 1706 where the rear caster
assemblies 1702a, 1702 have both dropped below the range of normal
operating positions. This condition may occur when the wheelchair
exhibits a tipping behavior. When both of the rear caster assemblies
1702a, 1702b have dropped below the range of normal operating positions,
the biasing members 1708a, 1708b both extend to a relaxed state and may
pull the trigger actuating members 1708a, 1708b out of engagement with
the sensors or triggers 1704a, 1704b to place the sensors or triggers in
an engaged state. When one or more of the caster assemblies 1702a, 1702b
return to a normal operating position with respect to the frame 1701,
both sensors or triggers are returned to the disengaged state.

[0096]FIGS. 20, 21 and 22 illustrate an embodiment of a rear caster
suspension 2000 and rear caster position sensing arrangement 2006 where
movement of one caster assembly 2002a is limited, depending on the
position of the second caster assembly 2002b. The rear caster suspension
includes a pair of rear caster assemblies 2002a, 2002b, a pair of sensors
or triggers 2004a, 2004b, the rear caster position sensing arrangement
2006, and a pair of biasing members 2008a, 2008b, such as springs or
other resilient members. In the example illustrated by FIGS. 20, 21 and
22, compression springs are schematically represented. However, extension
springs can be used, or the biasing members can take some other form.
Each rear caster assembly 2002 includes a caster 2010, a pivot arm 2012a,
2012b, and a stop member 2013a, 2013b attached to the pivot arm. The
pivot arms 2012 are coupled to a wheelchair frame 2001 at pivots 2016a,
2016b (See FIG. 20B). The stop members 2013a, 2013b rotate with the pivot
arms 2012a, 2012b about the pivots 2016a, 2016b. The sensors or triggers
2004a, 2004b are supported by the wheelchair frame 2001.

[0097]The illustrated rear caster position sensing arrangement 2006
includes a pair of spaced apart trigger actuating members 2020a, 2020b
that are coupled to the wheelchair frame 2001 at pivots 2022a, 2022b. The
elongated members 2020a, 2020b are connected together by a bar 2024. The
bar 2024 extends past the pivots 2022a, 2022b for selective engagement
with the stop members 2013a, 2013b. The biasing members 2008a, 2008b are
interposed between the rear caster assemblies 2002a, 2002b and the
trigger actuating members 2020a, 2020b.

[0098]The rear caster suspension 2000 and rear caster position sensing
arrangement 2006 operate to place the sensors in the disengaged and
engaged states based on the positions of the rear caster assemblies
2002a, 2002b. The rear caster suspension 2000 and rear caster position
sensing arrangement 2006 limit the relative positions of the rear caster
assemblies 2002a, 2002b. In one embodiment, the suspension arrangement
2000 does not include a rear caster position sensing arrangement, and the
sensors 2004a, 2004b are omitted. In this embodiment, the elongated
members 2020a, 2020b may be modified accordingly or replaced with a
different arrangement for coupling the biasing members 2008a, 2008b to
the bar 2024.

[0099]Referring to FIGS. 20A, 20B and 20C, when one or both of the rear
caster assemblies 2002a, 2002b are in normal operating positions relative
to the frame 2001, the biasing members 2008a, 2008b hold the trigger
actuating members 2020a, 2020b against the sensors or triggers 2004a,
2004b (or some other stop if the sensors are omitted). The trigger
actuating members 2020a, 2020b position the bar 2024 with respect to the
stop members 2013. As long as the force applied by one or more of the
biasing members 2008a, 2008b is sufficient to maintain the trigger
actuating members 2020a, 2020b against the sensors or triggers 2004a,
2004b, the position of the bar 2024 is fixed. When there is a gap 2025
(FIG. 20B) between the bar 2024 and the stop members 2013a, 2013b, the
caster assemblies 2002 are free to move upwardly and downwardly with
respect to one another.

[0100]FIGS. 21A and 21B illustrate the situation where the rear caster
assembly 2002b drops, such that the stop member 2013b rotates into
contact with the bar 2024. When the stop member 2013b engages the bar
2024, further movement of the rear caster assembly 2002b is inhibited by
the bar. Referring to FIGS. 22A and 22B, the bar 2024 prevents the caster
assembly 2002a from falling into a deep depression. The rear caster
assembly 2002a can be moved downward by applying a downward force
indicated by arrow 2050 in FIGS. 22A and 22B. The force is applied by the
stop member 2013b, to the bar 2024, and to the trigger actuating member
2020b. If the force applied to trigger actuating member 2020a is
sufficient to compress the biasing member 2008b, the trigger actuating
member 2020b moves toward the rear caster pivot arm 2012b. As a result,
the elongated members 2020a, 2020b may move away from the triggers or
sensors 2004a, 2004b. When both rear casters 1010 fall away from the
frame 2001, the sensors 2004a, 2004b are placed in the engaged state in
the same manner as described with respect to the rear caster suspension
and trigger arrangement 1700. When one or both of the rear casters are in
a normal operating position, the sensors 2004a, 2004b are placed in a
disengaged state in the same manner as described with respect to the rear
caster suspension and trigger arrangement 1700.

[0101]FIGS. 23 and 24 illustrate another embodiment of a rear caster
suspension 2300 with a rear caster position sensing arrangement 2306. The
rear caster suspension includes a rear caster assembly 2302, a pair of
sensors or triggers 2304a, 2304b, the rear caster position sensing
arrangement 2306, and a biasing member 2308, such as a spring. In the
example illustrated by FIGS. 23 and 24, a compression spring is
schematically represented. However, an extension spring can be used, or
the biasing member can take some other form.

[0102]The rear caster assembly 2302 includes a pair of casters 2310a,
2310b and a pivot arm 2312. The pivot arm 2312 includes a first member
2313 coupled to a wheelchair frame 2301 at a pivot 2316 (See FIG. 23B)
and a second member 2315 connected to the first member 2313, such that
the pivot arm 2312 has a generally "T-shaped" configuration. The castors
2310a, 2310b are connected to ends of the second member 2315 and are
rotatable with respect to the pivot arm 2312.

[0103]The sensors or triggers 2304a, 2304b are supported by the wheelchair
frame 2301. The illustrated rear caster position sensing arrangement 2306
includes a pair of spaced apart elongated members 2319a, 2319b (See FIG.
23A) that support a trigger actuating member 2320 and are coupled to the
wheelchair frame 2301 at pivots 2322a, 2322b. The rear caster position
sensing arrangement 2306 could also be configured to include only one
member (or any other number of members) member that supports the rear
caster position sensing arrangement 2306. The biasing member 2308 is
interposed between the rear caster assembly 2302 and the trigger
actuating member 2320.

[0104]The rear caster suspension 2300 with the rear caster position
sensing arrangement 2306 can be included on any type of wheelchair to
sense a tipping behavior and control one or more stabilizing members or
stabilizing assemblies. Referring to FIGS. 23A, 23B and 23C, when the
rear caster assembly 2302 is in a normal operating position relative to
the frame 2301, the biasing member 2308 is compressed between the trigger
actuating member 2320 and the rear caster pivot arm 2312. The biasing
members 2308 force the trigger actuating member 2308 into engagement with
both of the sensors or triggers 2304a, 2304b to place both of the sensors
in a depressed or disengaged state.

[0105]FIGS. 24A, 24B and 24C illustrate the rear caster suspension 2300
and the rear caster position sensing arrangement 2306 where one of the
rear casters 2310a of the rear caster assembly 2302a encounters a
depression in the support surface. Since both rear casters 2310a, 2310b
are coupled to a common pivot arm, the rear caster 2310a does not drop
into the depression. The biasing member 2308 remains compressed between
the trigger actuating member 2320 and the rear caster pivot arms 2312a.
The biasing member 2308 forces the trigger actuating member 1708 into
engagement with the sensors or triggers 2304a, 2304b. When the rear
caster assembly 2302 drops below the range of normal operating positions,
the biasing member 2308 extends to a relaxed state and may pull the
trigger actuating member 2308 out of engagement with the sensors or
triggers 1704a, 1704b to place the sensors or triggers in an engaged
state.

[0106]FIGS. 25A, 25B and 25C illustrate a rear caster suspension 2500 that
is a variation of the rear caster suspension 2300 where the second member
2315 of the pivot arm is pivotally connected to the first member 2313 by
a pivotal connection 2500. The pivotal connection allows the ends of the
second member 2315 and the attached rear casters 2310a, 2310b to move
upward and downward with respect to one another. When one rear caster
2310a moves down, the other rear caster 2310b moves up.

[0107]Stability systems can be used on a wide variety of vehicles. When
used on wheelchairs, the wheelchairs may include front caster pivot arms
of any configuration. The front caster pivot arms may be coupled to drive
assemblies or the front caster pivot arms may be independent of the drive
assemblies (See FIGS. 1A, 1B, 1C). The front caster pivot arms can be
coupled to the drive assemblies in a wide variety of different ways. For
example, the front caster pivot arms can be coupled to the drive assembly
in any manner that transfers motion of the drive assembly to the front
caster pivot arm, including but not limited to, a fixed length link, a
variable length link, a flexible link, a chain, a cord, a belt, a wire, a
gear train, or any other known structure for transferring motion from one
structure to another structure. FIGS. 26-31 illustrate one side of
wheelchairs with stability systems and pivot arms that are coupled to a
drive assembly. The other side is a mirror image in the exemplary
embodiment and is therefore not described in detail.

[0108]FIG. 26 schematically illustrates a mid-wheel drive wheelchair 2600
that includes a tip or stability control system that comprises at least
one tip sensor or trigger 2612 and at least one stabilizing member or
assembly 2614. The wheelchair 2600 includes front caster pivot arms 2608
that are coupled to drive assemblies 2606. Each drive assembly 2606
includes a drive wheel 2615 and a motor or drive 2617 that propels the
drive wheel 2615. The drive 2617 may comprise a motor/gear box
combination, a brushless, gearless motor, or any other known arrangement
for driving the drive wheel 2615. The drive assembly 2606 is connected to
the frame 2602 at a pivotal connection 2619. In the example illustrated
by FIG. 26, the pivotal connection 2619 is disposed below a drive axis
2621 of the drive wheel 2615 when the wheelchair 2600 is resting on flat,
level ground.

[0109]A front caster pivot arm 2608 is connected to each drive assembly
2606. A front caster 2631 is coupled to each front caster pivot arm 2608.
The front caster 2631 is movable upwardly and downwardly as indicated by
double arrow 2616 by pivotal movement of the drive 2617 about the pivotal
connection 2619. Torque applied by the drive assembly 2606 urges the
front caster pivot arm 2608 and the front caster 2631 upward with respect
to a support surface 2633 as indicated by arrow 2635. In one embodiment,
the torque applied by the drive assembly 2606 lifts the front caster 2631
off the support surface 2633. In another embodiment, the torque applied
by the drive assembly 2606 urges the front caster 2631 upward, but does
not lift the front caster up off of the support surface.

[0110]Rear casters 2610 are coupled to the frame 2602 such that the rear
casters are moveable upwardly and downwardly with respect to the frame. A
stabilizing assembly 2614 is coupled to each front caster pivot arm 2618
and to the frame 2602. However, the stabilizing assembly can take any
form that allows the stabilizing assembly to inhibit tipping behavior.
One or more triggers or sensors 2612 may be coupled to rear caster pivot
arms 2620 to detect a tipping behavior of the wheelchair. However, a
trigger or sensor can be arranged in any manner to detect a tipping
behavior of the wheelchair and need not be coupled to a rear caster. The
trigger or sensor 2612 senses when conditions exist that may cause the
vehicle to exhibit a tipping behavior and causes the locking assembly
2614 to engage when a tipping behavior is sensed to prevent any further
tipping behavior.

[0111]FIG. 27 schematically illustrates a mid-wheel drive wheelchair 2700
that includes a tip or stability control system that comprises at least
one tip sensor or trigger 2712 and at least one stabilizing member or
assembly. The wheelchair 2700 is similar to the wheelchair 2600 of FIG.
26, but each front caster pivot arm 2708 includes upper and lower links
2710a, 2710b that define a four bar linkage. The upper link 2710a is
pivotally coupled to a caster support member 2711 at a pivotal connection
2780 and is fixedly connected to the drive 2617. The lower link 2710b is
pivotally coupled to the caster support member 2711 at a pivotal
connection 2782 and is pivotally connected to the frame 2701 at a pivotal
connection 2783.

[0112]The drive 2617, the links 2710a, 2710b, the frame 2701, and the
caster support member 2711 form a four-bar linkage. The pivotal
connections 2619, 2780, 2782, 2783 can be positioned at a wide variety of
different locations on the frame 2701 and the caster support member 2711
and the length of the links 2706 can be selected to define the motion of
the front caster as the front caster pivot arm 2708 is pivoted.

[0113]The rear casters 2710 are coupled to the frame 2701 such that the
rear casters are moveable upwardly and downwardly with respect to the
frame. A stabilizing assembly 2714 is coupled to each front caster pivot
arm 2718 and to the frame 2702. However, the stabilizing assembly can
take any form and be coupled in any manner that allows the stabilizing
assembly to inhibit tipping behavior. For example, a stabilizing assembly
2714 can be coupled to the drive 2617. One or more triggers or sensors
2712 are coupled to the rear caster pivot arms 2720 to detect a tipping
behavior of the wheelchair. However, a trigger or sensor can be arranged
in any manner to detect a tipping behavior of the wheelchair and need not
be coupled to a rear caster. The trigger or sensor 2712 senses when
conditions exist that may cause the vehicle to exhibit a tipping behavior
and causes the locking assembly 2714 to engage when a tipping behavior is
sensed to prevent any further tipping behavior.

[0114]FIG. 28 schematically illustrates a mid-wheel drive wheelchair 2800
that includes a tip or stability control system 2802 that comprises at
least one tip sensor or trigger 2812 and at least one stabilizing member
or assembly. Front caster pivot arms 2808 are coupled to drive assemblies
2806 by a link 2809. The wheelchair 2800 is similar to the wheelchair
2600 of FIG. 26, but the front caster pivot arm 2808 is pivotally coupled
to the frame 2801 and is coupled to the drive assembly 2806 by the link
2809. Each drive assembly 2806 is mounted to the frame 2801 by a pivot
arm 2820 at a drive assembly pivot axis 2822. The pivot arm 2820 extends
forward and downward from the motor drive to the drive assembly pivot
axis 2822. The pivot axis 2822 of the drive assembly pivot arm 2820 is
below the drive wheel axis of rotation 2830 and the axis 2832 of an axle
2834 that the front caster wheel 2836 rotates around.

[0115]In one embodiment, a biasing member, such as a spring may optionally
be coupled between the frame 2801 and the front caster pivot arm 2808
and/or the frame and the drive assembly 2806 to bias the front caster
into engagement with the support surface 2819 or a biasing member may be
included in the stabilizing assembly 2814. The front caster pivot arm
2808 is pivotally mounted to the frame at a pivot axis 2850. The pivot
axis 2850 of the front caster pivot arm 2808 is forward of the drive
assembly pivot axis 2822 and below the axis of rotation 2830 of the drive
wheel.

[0116]The link 2809 is connected to the drive assembly pivot arm 2820 at a
pivotal connection 2851 and is connected to the front caster pivot arm
2808 at a pivotal connection 2852. The link 2809 can take a wide variety
of different forms. For example, the link may be rigid, flexible, or
extendible in length. The link need not comprise a linear member for
example, the link may be a gear train. The link 2809 may be any
mechanical arrangement that transfers at least some portion of motion in
at least one direction of the drive assembly 2806 to the front caster
pivot arm 2808.

[0117]When the drive assembly 2806 is accelerated such that the moment arm
generated by drive wheel 2815 is greater then all other moment arms
around pivot axis 2822, the drive assembly 2806 pivots and pulls the link
2809. Pulling on the link 2809 causes the front caster pivot arm 2808 to
move upward or urges the pivot arm upward. When the link 2809 is a
variable length link, such as a spring, a shock absorber, or a shock
absorber with a spring return, the drive assembly 2806 pulls the link
2809 to extend the link to its maximum length or a length where the front
caster pivot arm 2808 begins to pivot. Once extended, the link 2809 pulls
the front caster pivot arm 2808 upward or urges the front caster pivot
arm upward.

[0118]Rear casters 2810 are coupled to the frame 2801 such that the rear
casters are moveable upwardly and downwardly with respect to the frame. A
stabilizing assembly 2814 is coupled to each front caster pivot arm 2808
and to the frame 2801, to the drive assembly 2806 and the frame 2801
and/or to the link 2809 and the frame 2801. However, the stabilizing
assembly can take any form and be positioned in any manner that allows
the stabilizing assembly to inhibit a tipping behavior. One or more
triggers or sensors 2812 are coupled to the rear caster pivot arms 2820
to detect a tipping behavior of the wheelchair. However, a trigger or
sensor can take any form and be arranged in any manner to detect a
tipping behavior of the wheelchair and need not be coupled to a rear
caster. The trigger or sensor 2812 senses when conditions exist that may
cause the vehicle to exhibit a tipping behavior and causes the locking
assembly 2814 to engage when a tipping behavior is sensed to prevent any
further tipping behavior.

[0119]FIG. 29 schematically illustrates a mid-wheel drive wheelchair 2900
that includes a tip or stability control system that comprises at least
one tip sensor or trigger 2912 and at least one stabilizing member or
assembly 2914. Front caster pivot arms 2908 are coupled to drive
assemblies 2906 by a link 2909. The wheelchair 2900 is similar to the
wheelchair 2800 of FIG. 28, but the front caster pivot arm 2908 and the
drive assembly pivot arm 2920 are disposed in a crossed configuration.

[0120]Each drive assembly 2906 is mounted to a frame 2901 by a pivot arm
2920 at a drive assembly pivot axis 2922. The pivot arm 2920 extends
forward and downward from the motor drive to the drive assembly pivot
axis 2922. The pivot axis 2922 of the drive assembly pivot arm 2920 is
below the drive wheel axis of rotation 2930. The front caster pivot arm
2908 is pivotally mounted to the frame at a pivot axis 2949. The pivot
axis 2949 of the front caster pivot arm 2908 is rearward of the drive
assembly pivot axis 2932 and below the axis of rotation 2930 of the drive
wheel. As such, the front caster pivot arm 2908 and the drive assembly
pivot arm 2920 are in a crossed configuration. The front caster pivot arm
2908 and the drive assembly pivot arm 2920 may be bent or may be offset
to accommodate the crossed configuration.

[0121]The link 2909 is connected to the drive assembly pivot arm 2920 at a
pivotal connection 2950 and is connected to the front caster pivot arm
2908 at a pivotal connection 2952. The link 2909 can take a wide variety
of different forms. Any link 2909 that transfers at least some portion of
motion in at least one direction of the drive assembly 2906 to the front
caster pivot arm 2908 can be used.

[0122]When the drive assembly 2906 is accelerated such that the moment arm
generated by a drive wheel 2915 is greater then all other moment arms
around pivot axis 2922, the drive assembly 2906 pivots and pulls the link
2909. Pulling on the link 2909 causes the front caster pivot arm 2908 to
move upward or urges the pivot arm upward.

[0123]Rear casters 2910 are coupled to the frame 2901 such that the rear
casters are moveable upwardly and downwardly with respect to the frame. A
stabilizing assembly 2914 is coupled to each front caster pivot arm 2908
and to the frame 2901, to the drive assembly 2906 and the frame 2901
and/or to the link 2909 and the frame 2901. One or more triggers or
sensors 2912 are coupled to rear caster pivot arms 2920 to detect a
tipping behavior of the wheelchair. However, a trigger or sensor can take
any form and be arranged in any manner to detect a tipping behavior of
the wheelchair and need not be coupled to a rear caster. The trigger or
sensor 2912 senses when conditions exist that may cause the vehicle to
exhibit a tipping behavior and causes the locking assembly 2914 to engage
when a tipping behavior is sensed to prevent any further tipping
behavior.

[0124]FIG. 30 schematically illustrates a mid-wheel drive wheelchair 3000
that includes a tip or stability control system that comprises at least
one tip sensor or trigger 3012 and at least one stabilizing member or
assembly 2914. Front caster pivot arms 3008 are coupled to drive
assemblies 3006 by a link 3009. The wheelchair 3000 is similar to the
wheelchair 2900 of FIG. 29, but the front caster pivot arm 3008 comprises
an upper link 3011a and a lower link 3011b.

[0125]The upper link 3011a is pivotally coupled to a caster support member
3013 at a pivotal connection 3015 and is pivotally connected to the frame
3001 at a pivotal connection 3017. The lower link 3011b is pivotally
coupled to the caster support member 3013 at a pivotal connection 3019
and is pivotally connected to the frame 3001 at a pivotal connection
3021.

[0126]The caster support member 3013 may be any structure that couples the
links 3011a, 3011b to be coupled to a front caster 3036. The links 3011a,
3011b, the frame 3001, and the caster support member 3013 form a four-bar
linkage. The pivotal connections 3015, 3017, 3019, 3021 can be positioned
at a wide variety of different locations on the frame 3001 and the caster
support member 3013 and the length of the links 3011a, 3011b can be
selected to define the motion of the caster 3036 as the front caster
pivot arm 3008 is pivoted. In the example illustrated by FIG. 30, the
front caster pivot arm 3008 retracts the front caster 3008 or pivots the
wheel of the front caster toward the frame as the pivot arm 3008 is
lifted and extends the front caster or pivots the wheel of the front
caster away from the frame as the front caster pivot arm is lowered.

[0127]Each drive assembly 3006 is mounted to the frame 3001 by a pivot arm
3020 at a drive assembly pivot axis 3022. The pivot arm 3020 extends
forward and downward from the motor drive to the drive assembly pivot
axis 3022. The pivot axis 3022 of the drive assembly pivot arm 3020 is
below the drive wheel axis of rotation 3030 and is in front of the front
caster pivot anus 3008. As such, the front caster pivot arm 3008 and the
drive assembly pivot arm 3020 are in a crossed configuration. The front
caster pivot arm 3008 and the drive assembly pivot arm 3020 may be bent
or may be offset to accommodate the crossed configuration.

[0128]The link 3009 is connected to the drive assembly pivot arm 3020 at a
pivotal connection 3050 and is connected to the front caster pivot arm
3008 at a pivotal connection 3052. The link 3009 can be connected to the
upper link 3011a, or the lower link 3011b. Any link 3009 that transfers
at least some portion of motion in at least one direction of the drive
assembly 3006 to the front caster pivot arm 3008 can be used.

[0129]When the drive assembly 3006 is accelerated the drive assembly 3006
may pivot and pull the link 3909. Pulling on the link 3009 causes the
front caster pivot arm 3008 to move upward or urges the pivot arm upward.

[0130]Rear casters 3010 are coupled to the frame 3001 such that the rear
casters are moveable upwardly and downwardly with respect to the frame. A
stabilizing assembly 3014 is coupled to each front caster pivot arm 3008
and to the frame 3001, to the drive assembly 3006 and the frame 3001
and/or to the link 3009 and the frame 3001. One or more triggers or
sensors 3012 are coupled to rear caster pivot arms 3020 to detect a
tipping behavior of the wheelchair. However, a trigger or sensor can take
any form and can be arranged in any manner to detect a tipping behavior
of the wheelchair and need not be coupled to a rear caster. The trigger
or sensor 3012 senses when conditions exist that may cause the vehicle to
exhibit a tipping behavior and causes the locking assembly 3014 to engage
when a tipping behavior is sensed to inhibit further tipping behavior.

[0131]FIG. 31 schematically illustrates a mid-wheel drive wheelchair 3100
that includes a tip or stability control system that comprises at least
one tip sensor or trigger 3112 and at least one stabilizing or assembly
3114. Front caster pivot arms 3108 are coupled to drive assemblies 3106
by a link 3109. The wheelchair 3100 is similar to the wheelchair 2800 of
FIG. 28, but the front caster pivot arm 3108 and the drive assembly 3106
are pivotally coupled to the frame 3101 at a common pivot axis 3122.

[0132]Each drive assembly 3106 is mounted to the frame 3101 by a pivot arm
3120. The pivot arm 3120 extends forward and downward from the motor
drive to the common pivot axis 3122. The pivot axis 3122 is below the
drive wheel axis of rotation 3130 and the axis 3132 that the front caster
wheel 3136 rotates around.

[0133]The link 3109 is connected to the drive assembly pivot arm 3120 at a
pivotal connection 3150 and is connected to the front caster pivot arm
3108 at a pivotal connection 3152. The link 3109 can take a wide variety
of different forms. For example, the link may be rigid, flexible, or
extendible in length. Any link 3109 that transfers at least some portion
of motion in at least one direction of the drive assembly 3106 to the
front caster pivot arm 3108 can be used.

[0134]When the drive assembly 3106 is accelerated, the drive assembly 3106
may pivot and pull on the link 3109. Pulling on the link 3109 causes the
front caster pivot arm 3108 to move upward or urges the pivot arm upward.

[0135]Rear casters 3110 are coupled to the frame 3101 such that the rear
casters are moveable upwardly and downwardly with respect to the frame. A
stabilizing assembly 3114 is coupled to each front caster pivot arm 3108
and to the frame 3101, to the drive assembly 3106 and the frame 3101
and/or to the link 3109 and the frame 3101. However, the stabilizing
assembly can take any form and be positioned in any manner that allows
the stabilizing assembly to inhibit tipping behavior. One or more
triggers or sensors 3112 are coupled to the rear caster pivot arms 3110
to detect a tipping behavior of the wheelchair. However, a trigger or
sensor can take any form and be arranged in any manner to detect a
tipping behavior of the wheelchair and need not be coupled to a rear
caster. The trigger or sensor 3112 senses when conditions exist that may
cause the vehicle to exhibit a tipping behavior and causes the locking
assembly 3114 to engage when a tipping behavior is sensed to prevent any
further tipping behavior.

[0136]FIGS. 32-37 illustrate an example of a mid-wheel drive wheelchair
3200 that includes a control system that comprises sensors or triggers
3212a, 3212b and stabilizing members 3214a, 3214b. The wheelchair 3200
includes a frame 3202, a seat (not shown) is supported by the frame 3202,
first and second drive assemblies 3206a, 3206b, first and second front
caster pivot anus 3218a, 3218b, first and second front casters 3208a,
3208b, first and second rear caster pivot arms 3220a, 3220b, and first
and second rear casters 3210a, 3210b. A rear caster position sensing
arrangement 4400 (see FIGS. 44-51) communicates a condition of the rear
caster pivot arms 3220a, 3220b to both of the sensors or triggers 3212a,
3212b.

[0137]Referring to FIG. 32, the illustrated frame 3202 is made from
sheetmetal panels, but can be constructed in any manner that is suitable
for the application of the wheelchair 3200. The illustrated frame 3202
defines an interior space 3203 for batteries (not shown), wiring (not
shown), and other wheelchair components.

[0138]Referring to FIGS. 32 and 33, each drive assembly 3206a, 3206b
includes a drive wheel 3215 and a motor or drive 3217 that propels the
drive wheel 3215. The drive 3217 may comprise a motor/gear box
combination, a brushless, gearless motor, or any other known arrangement
for driving the drive wheel 3215. The drive 3717 is coupled to the frame
3202 at a pivotal connection 3219. The pivotal connection 3219 is
disposed below a drive axis 3221 of the drive wheel 3215 when the
wheelchair 3200 is resting on flat, level ground. FIGS. 38-41 show the
wheelchair 3200 with many of the components removed to more clearly
illustrate the drive 3217, the front pivot caster pivot arm 3218a, the
rear caster pivot arm 3220a, and the stabilizing member 3214a mounted on
one side of the frame 3202. The component mounting on the other side of
the frame 3202 may be a mirror image, and is therefore not described in
detail.

[0139]Referring to FIG. 39, each front caster pivot arm 3218a, 3218b
includes upper and lower links 3223a, 3223b that define a four bar
linkage. The upper link 3223a is pivotally coupled to a caster support
member 3211 at a pivotal connection 3280 and is fixedly connected to the
drive 3217. The lower link 3223b is pivotally coupled to the caster
support member 3211 at a pivotal connection 3282 and is pivotally
connected to the frame 3202 at a pivotal connection 3283. The drive 3217,
the links 3223a, 3223b, the frame 3202, and the caster support member
3211 form a four-bar linkage.

[0140]The front caster 3208a is coupled to the caster support member 3211.
The front caster pivot arms 3218a, 3218b are independently pivotable
upwardly and downwardly on the opposite sides of the frame to move the
front casters 3208a, 3208b upwardly and downwardly with respect to the
frame 3202.

[0141]Referring to FIGS. 33 and 39, when the drive assembly 3206a is
accelerated such that the moment arm generated by drive wheel 3215 is
greater then all other moment arms around pivot axis 3219, the drive
assembly 3206 pivots about pivot axis 3219 to move the front caster pivot
arm 3218 upward or urges the pivot arm upward as indicated by arrow 3301.
Resulting upward tendencies of the front caster 3208a helps the
wheelchair 3200 to traverse obstacles. In the exemplary embodiment, the
drive assembly 3206b operates in the same manner or a similar manner to
move or urge the front caster 3208b upward.

[0142]Referring to FIGS. 40-42, the stabilizing member 3214a comprises a
hydraulic cylinder with a spring return (see also FIGS. 5 and 6). The
stabilizing member 3214a includes a housing 4004, and a rod 4008. In this
embodiment, the sensor or trigger 3212a is a portion of a button 4006
that extends from the stabilizing member 3214a. The position of the
button 4006 determines the state of the stabilizing member 3214a. In the
wheelchair 3200, when the button 4006 is depressed, the rod 4008 may move
into and out of the housing 4004 to extend and shorten the length of the
stabilizing member 3214a. When the button 4006 is extended, the rod 4008
may move out of the housing 4004 to extend the length of the stabilizing
member 3214a, but is prevented from moving into the housing 4004 to
shorten the length of the stabilizing member. When the button 4006 is in
the depressed position, the movement of the fluid in the stabilizing
member 3214a when the rod extends and retracts provides a damping effect.
When the button 4006 is extended, the stabilizing member damps downward
movement of the front caster. In the wheelchair 3200, a spring return
(See FIG. 6) biases or returns the rod 4008 to an extended position to
bias the front caster toward contact with the ground.

[0143]Referring to FIGS. 40 -42, the stabilizing member 3214a is pivotally
connected to the frame 3202 at a pivotal connection 4020 and to the drive
assembly/front caster pivot arm at a pivotal connection 4022. When the
button 4006 is extended, the stabilizing member 3214a can extend to allow
the front caster to move downward with respect to the frame 3202, but
cannot retract to prevent upward movement of the front caster with
respect to the frame. When the button 4006 is depressed, the stabilizing
member 3214a allows the front caster to move upward and downward with
respect to the frame.

[0144]Referring to FIG. 42, the pivotal connection 4020 may comprise a
ball 4030 and socket 4032 connection. The ball 4030 is mounted to the rod
4008. The socket 4032 is connected to the frame 3202. If the pivotal
connection 4020 is made before the pivotal connection 4022, the ball 4030
can be turned in the socket 4032 to facilitate alignment required to make
the pivotal connection 4022. If the pivotal connection 4022 is made
before the connection 4022, the ball 4030 can be assembled in the socket
4022, regardless of the orientation of the ball with respect to the
socket. As a result, assembly of the stabilizing members 3214a, 3214b to
the frame and to the drive assembly/front caster pivot arm is made
easier.

[0145]In the embodiment of wheelchair 3200, optional vibration damping
assemblies 4250 are coupled to the button 4006 of each stabilizing member
3214a, 3214b to prevent vibration of the button 4006 in the rod 4008.
FIG. 42 illustrates a vibration damping assembly 4250 that includes a
ball portion for a ball and socket connection. FIG. 43 illustrates a
vibration damping assembly 4250 where the ball is omitted and the
stabilizing member 3214a is connected to the frame by a conventional
pivotal coupling or the ball is coupled to the stabilizing member at
another location. The vibration damping includes a housing 4212, a
trigger extension member 4214, and a biasing member 4216, such as a
spring or other resilient member. The housing 4212 is disposed on the end
of the rod 4008. In the embodiment illustrated by FIG. 42, the ball 4030
is defined as part of the housing 4212. In the embodiment illustrated by
FIG. 43, the housing 4212 does not include a ball portion. The trigger
extension member 4214 is disposed in the housing 4212 in engagement with
the control rod 4210. The biasing member 4216 biases the trigger
extension member 4214 against the button 4006. The biasing member 4216
applies a preload to the button 4006 to inhibit vibration of the button
4006 in the rod 4008. The force applied by the biasing member 4216 is
small enough that the biasing member 4216 does not depress the control
rod 4210 to a point where the stabilizing member 3214a, 3214 changes
state (i.e. from an engaged state to a disengaged state).

[0146]Referring to FIGS. 36 and 37, each rear caster pivot arm 3220a,
3220b is independently coupled to the frame 3202 at a pivotal connection
3602a, 3602b. Each rear caster 3210a, 3210b is coupled to a rear caster
pivot arm 3220a, 3220b, such that each rear caster can rotate around a
substantially vertical axis. FIGS. 44-50 illustrates the rear caster
position sensing arrangement 4400 and a rear caster suspension 4402 of
the wheelchair 3200. The rear caster suspension 4402 includes the rear
caster pivot arms 3220a, 3220b, the rear casters 3210a, 3210b, and
biasing members 4408a, 4408b, such as a spring or other resilient member.
A stop member 4413a, 4413b is attached to each pivot arm. The stop
members 4413a, 4413b rotate with the pivot arms 3220a, 3220b. The rear
caster position sensing arrangement 4400 includes a pair of spaced apart
trigger engagement assemblies 4420a, 4420b that are coupled to the
wheelchair frame at pivotal connections 4422a, 4422b. In the illustrated
embodiment, each rear caster position sensing arrangement includes an
elongated member 4423 pivotally coupled to the frame, and an adjustable
trigger engagement member 4425 connected to the elongated member 4423.

[0147]The adjustment between the engagement member 4425 and the elongated
member 4423 allows the amount of rotation of the rear caster position
sensing arrangement that causes engagement of the stabilizing members to
be adjusted. Referring to FIGS. 45 and 46, the distance that the
engagement members 4325 extend from the elongated members 4323 is
adjustable. The distance that the engagement members 4325 extend from the
elongated members determines the amount of rotation of the rear caster
position sensing arrangement that is required to cause the stabilizing
assemblies to engage and disengage. In another embodiment, the trigger
engagement assemblies 4420a, 4420b are replaced with the single piece
trigger engagement members.

[0148]In the embodiment illustrated by FIGS. 44-50, the pivotal
connections 4422a, 4422b are coaxial with pivotal connections 3602a,
3602b of the rear caster pivot arms. In another embodiment, the pivotal
connections 4422a, 4422b are offset form the pivotal connections 3602a,
3602b. The elongated members 4420a, 4420b are connected together by a bar
4424. Referring to FIGS. 45 and 51, the bar 4424 is disposed between
first and second engagement surfaces 4430, 4432 of the stop members
4413a, 4413b. The bar 4424 selectively engages the stop members 4413a,
4413b to limit relative movement between the first and second rear caster
pivot arms 3220a, 3320b. The biasing members 4408a, 4408b are interposed
between the rear caster pivot arms 3220a, 3220b and the elongated members
4420a, 4420b.

[0149]The rear caster position sensing arrangement 4400 operates to cause
both sensors or triggers to place both of the stabilizing members 3214a,
3214b in the engaged and disengaged states based on the positions of the
rear caster pivot arms 3320a, 3320b. FIG. 49 illustrates rear caster
pivot arm 3320a in a normal operating position. Rear caster pivot arm
3320b is not visible in FIG. 49, because it is in the same, normal
operating position, as rear caster pivot arm 3320a. When (shown
schematically in FIG. 49)one or both of the rear caster pivot arms 3320a,
3320b are in normal operating positions relative to the frame 3202, one
or more of the biasing members 4408a, 4408b hold both of the trigger
engagement assemblies 4420a, 4420b against both of the sensors or
triggers 3212a, 3212b, such that both stabilizing members are disengaged.
The elongated members 4420a, 4420b position the bar 4424 with respect to
the stop members 4413a, 4413b. As long as force applied by one or more of
the biasing members 4408a, 4408b is sufficient to maintain the elongated
members 4420a, 4420b against the sensors or triggers 3212a, 3212b, the
position of the bar 4424 is fixed. When there is a gap between the bar
4424 and a stop member 4413a, 4413b, the rear caster pivot arms 3320a,
3320b are free to move upwardly and downwardly with respect to one
another.

[0150]In FIGS. 44 and 49, the stop members 4413a, 4413b are in contact
with the bar 24. When the stop members 4413a, 4413b engage the bar 4424,
further relative movement of the of the rear caster pivot anus is
inhibited by the bar 4424. In the position shown by FIGS. 44 and 49, the
bar 4424 is in engagement with the engagement surface 4430 of both of the
stop members. As a result, downward movement of only one pivot arm 3320a,
3320b (with the other pivot arm remains in the position illustrated by
FIGS. 44 and 49) is inhibited by the bar 4024 and the biasing member
4408a or 4408b of the other pivot arm. However, both pivot arms 3320a,
3320b can pivot downward together relative to the frame. Referring to
FIG. 49A, downward movement indicated by arrow 4902 of both pivot arms
3220a (3220b is hidden) allows the rear caster position sensing
arrangement 4400 to move away from both of the triggers 3212a, 3212b,
allows the triggers to extend, and causes both of the locking members
3214 to disengage. As such, the rear caster pivot arms 3320a, 3320b move
independently from the position shown in FIG. 49 in the direction of
arrow 4904. Movement of each rear caster pivot arms 3320a, 3320b from the
position shown in FIG. 49 in the direction indicated by arrow 4902 is
dependent on the other rear caster pivot arm also moving in the direction
indicated by arrow 4902.

[0151]Referring to FIG. 41, each stabilizing member 3214a (3214b not
shown) is coupled to the frame 3202 and the front caster pivot arms
3218a, 3218b. The stabilizing members 3214a (3214b not shown) allow
upward and downward movement of the first and second front caster pivot
arms 3218a, 3218b relative to the frame 3202 when first and second rear
casters 3210a, 3210b are each in a normal position relative to the frame
shown in FIG. 41, because the rear caster position sensing arrangement
4400 engages both of the triggers 3212a, 3212b of the stabilizing members
3214a, 3214b in this position.

[0152]When the wheelchair 3200 exhibits a tipping behavior, the frame 3202
of the wheelchair is pitched slightly forward toward the front casters
3208a, 3208b. As a result, both of the rear casters 3320a, 3320b move
downward relative to the frame 3202 to maintain contact with the ground.
This downward movement moves the rear caster position sensing arrangement
4400 away from the triggers 3212a, 3212b, allows the triggers to move to
the extended position and causes the stabilizing assemblies 3214a, 3214b
to engage. In an exemplary embodiment, the stabilizing assemblies 3214a,
3214b engage to lock the first and second front casters 3208a, 3208b
against upward movement relative to the frame, but allow the front
casters to move downward when engaged. The stabilizing assemblies 3214a,
3214b may be configured in any manner that inhibits further tipping of
the wheelchair frame when the stabilizing members are engaged. In another
embodiment, the stabilizing assemblies 3214a, 3214b lock the front caster
pivot arms against both upward and downward movement with respect to the
pivot arm when engaged. When one or more of the rear casters return to a
normal operating position relative to the frame, the triggers are
depressed again to disengage and allow upward and downward movement of
the front casters relative to the frame. In the wheelchair 3200, the rear
caster position sensing arrangement is configured such that movement of
one of the rear casters to a normal operating position moves the other
rear caster up as well.

[0153]While the present invention has been illustrated by the description
of embodiments thereof, and while the embodiments have been described in
considerable detail, it is not the intention of the applicant to restrict
or in any way limit the scope of the appended claims to such detail.
Additional advantages and modifications will readily appear to those
skilled in the art. For example, pivotal connections can be made of any
number of structures including bearing assemblies, pins, nuts and bolts,
and frictionless sleeve assemblies. Additionally, springs or shock
absorbers can be added between pivoting and non-pivoting components to
limit, dampen, or somewhat resist the pivotal motions of these
components. Also, a brake-disc locking mechanism could be integrated into
any of the pivotal connections and serve as a stabilizing member or
assembly that locks components coupled to the pivotal connection from
rotation when actuated and freely allows pivotal motion about the
connection when not actuated. Therefore, the invention, in its broader
aspects, is not limited to the specific details, the representative
apparatus, and illustrative examples shown and described. Accordingly,
departures can be made from such details without departing from the
spirit or scope of the applicant's general inventive concept.